When bacteria evade host defenses and enter the blood stream, the clinical syndrome of sepsis ensues. Although bacteria can directly damage host tissues, an over exuberant inflammatory response to bacteria is more commonly the cause of organ failure and death during infection. Sepsis afflicts over 700,000 people yearly in the United States and leads to more than 200,000 deaths. Current treatments for sepsis include early antibiotics and aggressive intravenous fluids. However, treatments aimed at calming the immune response that leads to organ damage have not been successful. New therapeutic strategies based on novel biologic discoveries are needed in order to improve mortality from this common and devastating illness. Mounting evidence indicates that nerves send signals to immune cells and that these signals regulate how immune cells respond to various stimuli. The goal of this research proposal is to investigate how nerves regulate the immune system during sepsis. Specifically, this research proposal aims to identify how the sympathetic nervous system, which leads to the fight or flight response, alters survival during infection. Preliminar studies indicate that decreasing the release of norepinephrine, a compound released from sympathetic nerves during stress, improves survival in mouse models of infection. The goal of the 3 research aims is to systematically investigate how norepinephrine and innate immune cells, like macrophages, interact during infection. Specifically, aim 1 will investigate how ablatin of norepinephrine alters hemodynamics in mice and rats. Aim 2 will identify the cellular receptors on macrophages that help stress hormones signal to immune cells. Lastly, the goal of aim 3 is to determine how the signaling pathways that detect stress hormones interact with the signaling pathways that detect bacteria. Survival studies and measures of host response to infection (bacterial loads, cell counts, inflammatory cytokines), will be performed in order to investigate these aims. In addition, macrophages grown in cell culture will be used to study the receptors and molecules through which norepinephrine influences macrophages function. Finally, the relevance of all of these cell culture findings will be tested in mouse models of infection using bone marrow transplants and transgenic mice. The long-term goal of the proposed research is to identify new biologic mechanisms that might translate into novel therapies for sepsis. These studies may also illustrate how the systemic administration of exogenous norepinephrine, which is commonly used to increase blood pressure in critically ill patients, alters immunity. Lastly, these studies may shed light on how chronic physiologic or psychologic stress alter susceptibility to infection.